Earth’s mysterious large Moon is our nearest neighbor in space, dominating our clear night sky with its beguiling and bewitching cold golden glow. Earth’s Moon is the only body beyond our planet that we have visited, leaving our footprints embedded in its alien dust. Despite its close proximity to our planet, our mysterious Moon has still managed to keep some ancient secrets from us very well. However, in October 2014, using data derived from NASA’s Gravity Recovery and Interior Laboratory (GRAIL) mission, a team of planetary scientists announced that they may have solved a lunar mystery almost as old as our Moon itself.
First launched as GRAIL A and GRAIL B in September 2011, the two probes, playfully dubbed Ebb and Flow, operated in an almost-circular orbit near the lunar poles at an altitude of about 34 miles until their mission concluded in December 2012. The distance between the twin probes altered slightly as they flew over areas of lesser or greater gravity that resulted from visible features–such as craters and mountains–as well as by hidden masses secreted beneath our Moon’s surface.
The twin spacecraft flew in an almost-circular orbit until the mission ended on December 17, 2012, when the probes were intentionally sent down to the lunar surface. NASA ultimately named the impact site in honor of the late astronaut Sally K. Ride, who was America’s first woman in space and a member of the GRAIL mission team.
GRAIL’s main and extended science missions generated the highest resolution gravity field map of any celestial body. The map will provide a better scientific understanding of how our planet and other rocky planets in our Sun’s family were born and later evolved.
Earlier theories suggested that the craggy outline of a region of the lunar surface, named Oceanus Procellarum–or the Ocean of Storms–had resulted from a large asteroid impact. If this theory had been correct, the basin it had dug out would represent the largest asteroid impact basin scarring the lunar surface. However, mission scientists, scrutinizing GRAIL data, now believe that they have discovered new evidence that the craggy outline of this rectangular region–approximately 1,600 miles across–was actually caused by the formation of ancient rift valleys.